Traffic lights are devices which are installed at crossroads or crosswalks on roads and which indicate stop, detour, traveling, and the like to passing vehicles or pedestrians by flickering of red light, green light, yellow light, green arrow light, and the like.
With an exponential increase of vehicles, traffic congestion has become serious problems. The vehicle stop time due to traffic lights at downtown crossroads or crosswalks occupies a considerable ratio of the congestion rate due to various factors of roads. Therefore, it has been thought that the traffic congestion could be released by controlling signal light cycles of traffic lights at crossroads or crosswalks so as to improve traveling of vehicles, and various countermeasures have been proposed for this purpose.
Traffic light controllers are connected to a traffic control center via a network and changes signal light in accordance with a control signal output from the traffic control center to adjust a flow of vehicles. In the related art, the traffic tight controllers and the traffic control center are connected to each other via a wired network using exclusive lines. Since the traffic control center and the traffic light controllers communicate with each other in a one-to-one manner, the traffic control center needs a complicated system to transmit different control commands to all the traffic light, controllers. In addition, since the traffic control center has to finish communications with all the traffic light controllers within a predetermined time, the system or the wired network, using exclusive lines should be kept at a high speed and thus much cost such as facility cost, communication cost facility maintenance cost, and network maintenance cost, is consumed.
Therefore, in general only the traffic light controllers controlling traffic lights installed in important road zones such as crossroads are connected to the traffic control center, in this case, in the traffic light controllers installed out of the important road zones such as crossroads, the cycle of a signal light changing operation is set to be constant and the signal light is changed with a predetermined cycle to adjust, a flow of vehicles. That is, the traffic light controllers other than the traffic light controllers connected to the traffic control center operate without any interlock with rite control of the traffic control center.
As described above, since only the traffic light controllers connected to the traffic control center via exclusive lines perform a signal light changing operation on traffic lights on the basis of traffic information based on traffic conditions to control a flow of vehicles and the other traffic light controllers perform the signal light, changing operation with a predetermined signal light change cycle, there is a problem in that signal light of all the traffic lights cannot be controlled as a whole and thus a flow of vehicles cannot be smoothly controlled.
As a solution to this problem, Korean Patent Application Publication No, 10-2001-0100275 filed by the applicant of the present invention discloses traffic light control device and method of controlling a signal light changing operation by causing a traffic control center to selectively output a control signal for controlling traffic light controllers in a wireless manner. The applicant of the present invention has filed a lot of patent applications such as Korean Patent Application Publication No. 10-2006-0129993. However, in this case, different controls signals have to be generated and output to control a lot of traffic light controllers.
In the related art, Korean Patent Application Publication No. 10-2009-0008964 discloses a traffic light control device for smoothing a traffic flow in consideration of the number of vehicles by periodically counting passing vehicles, increasing a lighting time of a blue light when the number of vehicles increases, and decreasing the lighting time of a blue light when the number of vehicles decreases. In this case, a sensor unit for detecting a toweling vehicle and a counter unit for counting the number of vehicles need to be provided to each traffic light control device and the traffic lights are controlled independently of the control of the traffic control center. Accordingly, there is a problem in that the traffic lights may operate regardless of traffic flows of other roads.